[PATCH] [Reassociation][PR21205] Don't canonicalize X - undef to X + (-undef).

[Chad Rosier]

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Comment at: test/Transforms/Reassociate/pr21205.ll:1
@@ +1,2 @@
+; RUN: opt < %s -reassociate -disable-output
+; PR21205
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I missed the FileCheck.. one moment.

http://reviews.llvm.org/D5674